Fail-safe catch



J. ,M MEEK ETAL FAIL-SAFE CATCH Aug. 6, 1957 Filed April 11. 1956 V 5%Kaxm CIRCUIT -7O FIRING INVENTOR. James M Mee/r By Harvey A. Foure m M m 9 w a W &

United States Patent Ofifice FAIL-SAFE CATCH James M. Meek, Silver Spring, and Harvey A. Foure,

Landover, Md., assignors to the United States of America as represented by the Secretary of the Army Application April 11, 1956, Serial No. 577,625 3 Claims. (Cl. 102-78) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to us of any royalty thereon. This invention relates to ordnance fuzes and more particularly to inertia devices for arming fuzes.

Fuzes for explosive ordnance projectiles are often armed by acceleration-responsive devices activated by setback-4. e., the acceleration occurring when the projectile is fired or launched. These acceleration-responsive devices are designed to arm a fuze when it is subjected to an acceleration over a certain period of time; the fuze is not responsive to acceleration caused from dropping but only from sustained accelerations as result from setback. An additional advantage of an accelerationresponsive arming system is that projectiles which have sustained propulsion, such as rockets, can be designed not to arm until some predetermined distance from the launch area.

Certain safety-and-arming mechanisms of the acceleration-responsive type include an escapement or other mechanism to slow down the relative motion of the acceleration-responsive weight. Failure of such mechanism would permit premature arming. The present invention provides an auxiliary safety device that positively prevents arming before sustained acceleration. The device of the invention is in effect a secondary acceleration-responsive device mounted on an element of the main acceleration-responsive device. Unless this secondary acceleration-responsive device is actuated by sutficient sustained acceleration, it positively prevents motion of the main acceleration-responsive device to the armed position.

An object of the invention is to provide a device for positively preventing the instantaneous arming of fuzes.

Another object is to provide such a device that is only slightly affected by side acceleration and is primarily responsive to axial acceleration.

Further objects are to achieve the above with a device that is sturdy, simple, and reliable, yet cheap and easy to manufacture.

The specific nature of the invention as well as other objects, uses and advantages thereof will clearly appear from the following description and from the accompanying drawing, in which:

Fig. 1 is an axial sectional view of a device in accordance with the invention with associated electrical circuits schematically shown.

Fig. 2 is a cross sectional view taken along the line 2-2 of Fig. 1.

Fig. 3 is an axial sectional view of a modification of a device in accordance with the invention, shown under the influence of acceleration.

In Figs. 1 and 2 a cylindrical weight is slidably positioned within a cavity 12 which consists of three concentric cylindrical bores 14, 16, and 18, contained in a housing 20. The bottom of the lower bore 14, which is of the same diameter as the weight 10, is closed by a plug 22 made of insulating material. This plug has a small aperture 24. To contain weight 10 within the cavity 12, the top of the upper bore 18 has a retaining ring 26. A light coil spring 28 holds weight 10 against ring 26.

The upper portion of weight 10 is cut away to form a fiat plate 30. This plate has two parallel pins 32 extending through it, about which pins are pivoted two masses 38 each having a catch 34. These masses 38 are geared to each other at 35 and are biased in an outward position by how spring 36. The masses 38 are so balanced that their center of gravity is located at CG as indicated.

Detonator 40 is normally shorted by frangible switch 42 which comprises a brittle insulator 44, such as glass or ceramic, with a line of metallic paint 46 on it. Frangible switch 42, which is known in the switch art, is connected at one side to ground through ring 26, on which it is located. The other side is connected through lead 48 to detonator 40. Shaft 50 is attached to top of weight 10 and extends through a close-fitting opening 52 in frangible switch 42.

When the housing 20 is accelerated in the direction of arrow a, weight 10 is moved in space in the same direction against inertia partially by spring 28 but primarily by the dash pot action of cylindrical weight 10 in bore 14 and restricted fluid passages 24 and 52. The function of weight 10 in relation to housing 20 is thus essentially that of an acceleration-responsive device. The function of masses 38 in relation to weight 10 is essentially that of a second acceleration-responsive device; if the acceleration of weight 10 is sufliciently great, catches 34 pivot inward against the bias of spring 36. With sustained acceleration sufiicient to keep catches 34 pivoted inward, catches 34 clear shoulder 54 between bores 16 and 18 permitting the continued motion of weight 10 in relation to housing 20, so that protuberance 56 on shaft 50 strikes and breaks frangible switch 42. Continued movement results in insulated end 58 of weight 10 closing switch 60, which consists of two contact armsa first arm 62 of resilient metal and a second arm 64 of ductile metal overlying the first. As will be seen, when the insulated end 58 pushes ductile arm 64 down on resilient arm 62 the switch will remain closed even after the pressure of weight 10 is removed. When closed, switch 60 connects detonator 40 to a firing circuit 70, which may be of a well-known type.

Thus it will be seen that the device is fail safe, for if the first acceleration-responsive device failsi. e., if weight 10 is not delayed in its movement relative to housing 20, catches 34 will remain in the extended posi tion and catch on shoulder 54.

For use on guided missiles the device must not be unduly sensitive to side thrust because these missiles often maneuver violently. The first acceleration-responsive device (weight 10 and cavity 12) will not be affect ed by side thrust unless this thrust is so much greater than the forward acceleration as to stop the device by friction. Because the two masses 38 of the second acceleration-responsive device are geared together it is isolated from side thrust. The thrust tending to cause one mass to move outward will cause the other to move inward, and as the two are identical, these two tendencies will cancel one another. If the centers of gravity CG of masses 38 were located on a line connecting the centers of pins 32, gearing them together would not be necessary and the device would also be unaffected by spin about its longitudinal axis. However, since the masses 38 must rotate about pins 32 it would not be possible to maintain the center of gravity on this line as the device operated.

In the embodiment of Fig. 3, drical'weight is partially in slidable elongated cylinbore 112 with the upper Patented Aug. 6, 1957 of weight 11 0.has-a coaxial bore 130.with three-ho les 132,- extending radially outward. Within'theseholes.132arev three. catches 134 which take the form, of spheres.

Catches '134 are normallyheld out, against walls of counterbore'118 by the sides of secondary'weight or m ss., 8, whi h s in, re 130. Mass 1.38..v is fitted into bore 130- so that it forms a1 dashpot; that, is, they pressure of, the air trapped below mass 138 prevents it moving downward relative to weight 110 until the air leaks" through the restricted passage between"th'e ,mass 138 and the walls of bore1'30. .Magnet 136 closes bore l30andnqrmallyrholds secondary weight 138 forward of that position shown in Fig.3.

When housing 120 .'s accelerated'forward inthe direction of arrow a, mechanism (not shown) suchas clockwork connected to pinion 124 retards the movement of weight 110 relative to housing 120, Another expression for this is that weight 1101 is accelerated forward in.

space by pinion 124, the rotation' restrained, A's weight 110 is accelerated forward, secondary weight 138 moves relative to it unlocking "catches 134 as shown in Fig! 3.' As theaccelerationcontinues, weight 110 continues to" move relative to -housirig 120', ultimately arming the, fuze through mechanism (also-not shown) operated by pinion 124. I

Ifv thedelay mechanism should fail, permitting weight 110 to remainstationary in space. as housing: 120 moves forward, then secondary weight 138 will also remain stationary and lock catches 134 in theoutward position,

where they "will catch' on frustro-conical surface 154.

between bores. 112 and 118. The conic angle of surface 154 is small so that catches 134 locksecondary weight 138, relative to weight 110. Unless the angle is small the device will act as a double element delay similar to Rabinows Double Element Setback Lock, U. S. Patent'2,625,881.

- Shaft 140 extends from the forward 'end' of secondary weight'138 toretain the catches 134 in position for assembly and resetting.

It will beseen that thedevice of Fig. 3 is also two acceleration-responsive devices. I

The 'firs t comprises 1 spending positions.

weight 110 and its associated retarding mechanism, not

shown; the second comprises secondary Weight 138 and the retarding force of magnet 136 and the dashpot action of cylindricalmass 138 in bore 130 with the restricted air passage between them. It is also fail-safe because if the first delay mechanism does not function the catches 134 will prevent arming.

It will be apparent that the embodiments shown are only exemplary and that various modifications can bev made in construction, materials, and arrangement within the scope of the invention as defined in the appended claims.

We claim:

1. A fail-safe catch device comprising: a housing; a weight mounted for movement in one path in the housing; means for retarding the movement of the'weight relative to the housing; means for halting the movement of the weight relative to the housing, said means for halting being responsiveto the failure of saidmeans for retarding; said means for halting includinga catch mounted on the weight,a mass mounted on the weight, and. a surface on the housing so that if the Weight is not accelerated, the catch willv engage thesurface and-halt the weight relative to'thehousing, said mass andcatch being a single member and thismember. being-pivoted to said axes normal to the direction of movement of said weight and means for causing said members 'to 'be in corre- 3. The invention as defined in claim Zwherein said means for causing'said membersto'be in corresponding positions include gears.

References Cited in the file of patent UNITED STATES PATENTS 2,436,396 McCaslin Febt'24, 1948 2,586,437 Rabinow Feb. 19, 1952 2,625,881 Rabinow IEIIL'ZO, 1953 2,685,253 Apothloz Aug. 3, 1954 

